1. Field of the Invention
This invention relates to a process to facilitate the removal of uranium during electrorefining, and, more specifically, this invention relates to a process for the generation of U+4 in an electrochemical cell.
2. Background of the Invention
Current United States policy is to store unprocessed spent reactor fuel in a geologic repository. Long-term uncertainties are hampering the acceptability and eventual licensing of geologic repositories for spent nuclear fuel in the U.S., and driving up its cost. The resistance to plans for depositing radioactive material in the Yucca Mountain Repository is a case in point.
Instead of long term storage of untreated radioactive materials, preliminary treat-ment of spent nuclear fuel is being explored, including partial utilization of the fissile material contained in the spent fuel. Accordingly, there is an emphasis upon developing new technologies for reprocessing and reutilizing spent nuclear fuels.
A number of processes exist for the processing and recycling of nuclear fuels. These processes often involve aqueous solutions. Due to the presence of water, aqueous solutions are neutron moderators. This is because collisions between water nuclei and neutrons, which are initially created by the spontaneous fission of plutonium, lowers the neutrons' kinetic energies. This lower energy increases the likelihood of the neutrons inducing more fission upon their collision with the plutonium nuclei remaining in the fuel. Thus, previously innocuous levels of plutonium now become potential run-away fission hazards. This lowered critical mass necessitates the use of very low plutonium concentrations and redundant safeguards to assure fission control. Lower plutonium throughputs result. Aqueous solution processing and recycling of nuclear fuels is generally inefficient and not cost-effective.
Electrorefining is a metallurgical separation technique that has been used to recover uranium from fission products and other components of spent fuel from the Experimental Breeder Reactor-II (EBR-II) of the Idaho National Engineering and Environmental Laboratory (INEEL), which is associated with Argonne National Laboratory-West (ANL-W). Electrorefining also is used to purify impure plutonium metal. Separation by electrorefining is based on changes in oxidation state and is accomplished by the addition or removal of electrons at electrodes, rather than the use of chemical oxidizing or reducing agents (aqueous or otherwise), which can significantly increase the volume of waste generated.
Interest in recent years has focused on the large inventory of blanket fuel and other spent metal fuels at DOE sites. (Blanket fuel contains primarily uranium-238, a non-fissile isotope that a reactor converts to fissionable plutonium. The blanket fuel is encased in steel cladding and is situated beyond the reactor core's outer edge and thus forms a “blanket” around the core.) A current method used for the recovery of unfissioned uranium from blanket fuels is the high-throughput electrorefiner (HTER) design.
U.S. Pat. No. 5,650,053 awarded to Gay, et al. on Jul. 22, 1997 discloses an electrorefining device and process for the recovery of uranium from spent nuclear fuel. The device consists of a hollow cylindrical-shaped cathode encased by rings of outer and inner anodic dissolution baskets.
U.S. Pat. No. 5,531,868 awarded to Miller, et al. on Jul. 2, 1996 discloses a device and a process for the electrorefining of spent nuclear fuel. The device comprises a hollow cathode such that a portion of the anode is near the cathode.
U.S. Pat. No. 5,009,752 awarded to Tomczuk, et al. on Apr. 23, 1991 discloses a device and a process for the recovery of uranium and plutonium from spent metal clad fuel pins. The process uses secondary reactions between U+4 cations and elemental uranium at the anode to increase reaction rates and improve anodic efficiency.
None of the aforementioned patents disclose an anodic device or method for the refinement and collection of uranium metal from spent nuclear fuels that facilitates the removal of uranium metal electrodeposited at the cathode without disruption of the normal electrorefining process.
A need exists in the art for a method and device for more efficient and more facile removal of uranium metal from the cathodes of electrorefiners. The method and device should not detract from the normal electrorefining process. Also, the method and device should not rely on the configuration, size or even the presence of the anode baskets in an electrorefiner.